With such pipes, cables, and ducts, there exists a problem of conserving the function for which they are designed (i.e. conveying a fluid under pressure, electrical energy, information, etc.) in the presence of fire and at relatively high temperatures, about 850.degree. C., and to continue doing so for a given length of time during which safety conditions are ensured.
One of the known existing solutions is that described in French patent application FR-86 17740, which is now French Patent 2,591,715, which solution is represented by a protective sheath comprising:
a wrapping comprising a plurality of layers of inorganic material;
a tight winding disposed over said wrapping and made of a thread or strip of material that withstands temperature; and
a sheath surrounding the winding and constituting a compression sleeve, the sheath also being made of a substance that withstands heat and/or fire.
More precisely, the above-mentioned inorganic material is constituted by mica which is supported by the inside face of a strip of glass silk, so as to facilitate application thereof around the pipe. The winding is constituted by strips of glass silk covered on their outside faces with aluminum so as to reflect heat. The sheath forming a compression sleeve is constituted by a woven cloth of material that withstands heat and/or fire. Between the winding and the compression sleeve, it is also possible to dispose a heat-distributing ceramic sheath made from threads of ceramic fibers, optionally coated in metal. An additional casing, in particular made of fire resistant silicone rubber and having tear strength may be applied to the outside of the above-described stratified protection structure for a pipe.
However, the above-outlined prior art solution suffers, like other prior art solutions, from the drawback of changing the pipe's own (static) flexibility, or in general, the flexibility of the elongate structure which is to be protected in this way. Further, these solutions increase dynamic stiffness and consequently noise generation in the event of vibration, and this can be unacceptable in some applications, particularly in submarines.
The object of the present invention is thus to provide a covering for an elongate structure such as pipework, electric or optical cables, and pneumatic or hydraulic ducting, which covering is more practical than previously known coverings for the same purpose, particularly in that, while ensuring that the structures continue to function for a given length of time as required for maintaining acceptable emergency conditions, it retains the static flexibility of the structures to be protected and provides little change to the dynamic stiffness thereof, producing little noise, even under difficult conditions of temperature, in particular when a fire breaks out, during which relatively high temperatures may be developed of about 850.degree. C. or even more, while not giving off toxic substances, in particular those based on halogens, phosphorus, etc. . . .